Ford 4600

after a judgement is done and wages being garnished,can u go back to court to try to ammend?

based on a wrong balance or financial hardship. This is for a car "voluntary surrender". Orig price 12000, I made 5600 in payments, they sold under book value for 4600. I was 3wks late on a payment from stipulation. they got judgement for 10,000. did not give me creit for $700 of payments. wages being garnished. If I Paid the 10k they will have recieved 21,000 for a 12k car. if this legal. Went through Ford Fairlane credit.
If u can go back to court for this ...where might I find the forms. new york State